Telephone system



Patented Jan, 12, 1943 2,307,818 TELEPHONE SYSTEM Charles Edmund Beale, Liverpool, England, as-

signor to Associated Telephone & Telegraph Company, Chicago, 111., a corporation of Delaware Application June 14, 1941, Serial No. 398,006 In Great Britain August 6, 1940 9 Claims.

The present invention relates to telephone sys-.

tems, and is more particularly concerned with direct current impulse repeating arrangements for use therein.

In a well-known form of such an arrangement, which may be inserted at the outgoing end of a line interconnecting two switching points, the incoming and outgoingsides are usually separated by line condensers, on the incoming side of which a battery feeding bridge is provided, while on the other side a supervision bridge is provided. The former bridge comprises a battery feeding impulse responding relay, a make contact of which is included in the outgoing side of the circuit to enable impulse repetition to be performed.

Such equipments give satisfactory service under normal line limits, but in cases where they have to meet widely varying conditions of operation such as when in association with either very short or very long lines, when operating at a tandem switching centre with connecting lines of widely varying length on either side thereof, or when two or more such repeaters are operated in tandem, the employment of this Stone bridge type of impulse repeater has not proved entirely satisfactory, in particular due to the distortion introduced by the charging and discharging of the separating condensers during impulsing.

In order to meet onerous operating conditions of the kind set forth above, it has been foundpreferable to replace the condensercoupling by repeating coils as the surge currents ar then more readily dealt with.

The chief object of the present invention is to provide an improved repeater of the type described in which difficulties tending to produce impulse distortion are overcome in a particularly simple manner.

Whenever battery feeding impulse repeaters are utilised under varying line limits of the kind that under impulse repetition conditions the ballast lamp connections are short-circuited. Preferably this is done by contacts of a slow releasing relay which is held operated while each incoming train of impulses is being received and which is released after each train to restore the normal connections of the battery feeding relay on to line for conversation conditions.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to theaccompanying drawing which shows a circuit diagram of an impulse repeater suitable for a long subscribers line which terminates in a private branch exchange board hereafter termed P. B. X board. This equipment provides a separate batteryv feed and impulse repetition facilities for such a line in order that through dialling can take place thereover on to the public automatic exchang into which the P. B. X board is assumed to operate.

Considering now the operation of the circuit, the negative and positive conductors on the right-hand side of the drawing connect withthe lon line extending to the subscribers station, while the negative and positive conductors on the left-hand side of the drawing terminate in a'jack on the P. B. X board.

Assuming that the subscribers line is directly connected through to the public automatic exchange over a patch cord at the P. B. X board, as may be the case under night switching conditions when the board is not attended, when the The object of the present invention, therefore,

is to remove the constant current device from the battery feed circuit during impulsing, in order to improve the impulse repetition characteristics of the repeater.

More specifically, it is arranged distant subscriber removes his receiver, the high impedance battery feeding impulse repeating relay A is operated over earth, lower winding of relay A, lower resistance element of the ballast lamp BRA, rectifier MRB, lower right-hand winding of the repeating coil RPC, conductor, calling subscribers loop, conductor, upper right-hand winding of repeatin coil RPC, rectifier MRA, upper resistance element of the ballast lamp BRA, upper winding of relay A, battery, and earth. Upon operation, relay A at armatur a! brings u the slow-to-release relay B. On the operation of this relay, a bridge is completed across the left-hand side of the line which extends from conductor, over contact a2, upper left-hand winding of repeating coil RPC, contact b2, lower left-hand winding of repeating coil RPC, to conductor. Thus, a seizing loop "is extended forward to the main exchange there by to prepare the switches therein t receive impulses. When the main exchange selector switches'are ready to receive impulses,

dial tone is returned to the calling subscriber, this tone extending through the equipment shown via the inductive coupling of the windings of the repeating coil, and the subscriber now proceeds to dial the required number.

Relay A responds to the first. train of'impulses received from the subscribers dial, and at armature a2 repeats those impulses to the main exchange. It will be noted that in order to reduce the period during which any surges which may result in the distortion of this first break period may be extended to line, armature a2'is.of the make-before-break type. and hence as soon" as relay A commences to release, the pubnc exchange side of the repeating coil is short-circuited over the partially released armature a? and operated armature bl. On the first release of relay A, an obvious circuit is closed for relay C, over contacts al and b3 and the two windings of relay C in series. Relay C operates a very short interval later and; at armature cl short v eircuitsthe back contact c2 thereby to maintain,

independently of contact a2, the short-circuiton the lefthand windings of the repeating coilvia armature bl so as to providean impedance-free repeating path to the public exchange. At armature 02 the right-hand low resistancewinding of relay is short-circuitedin order that relay C I maynow hold operated from the break pulses delivered by contact al for the duration of the impulse train. Relay B also holds operated durer and better impulsing limits can be obtained frorn the impulsing relay than were possible with the, ballast lamp, connectionsin circuit,

. The reason might be said to be that on very long lines theextra current receivedenables the relay to deliver a ,break impulseiwhich substantially corresponds with that delivered. from thedistant dial, Whereas without the short-circuiting of the ballast lamp the percentage .Of. the break to the .make ,periodas delivered from relay A. is. so

muchgincreasedv as. to necessitate a reduction in the allowable line resistance. ,Under Very short line conditions, althoughthe current through the Windings-Of relay A isgreater thanwiththe, ballastlamp in circuit, a satisfactory, impulsing response is still obtained since the Winding core, on which are situated a, number .of nickel-iron ,sleeves tor the purpose of maintaining a high impedance, exhibits asaturation efiectso that the magnetic flux produced without the ballast lamp circuit does not greatly exceed that obtaining with the lamp in circuit.

. It will thus be seen that the arrangement according to the invention whereby the, ballast resistance in circuit with the battery feed relay is I short-circuited under impulse repetition conditions is of particular advantage under long .line conditions, and it enables longer line limits to. be

obtained than has been hitherto possible with standard telephone type relays, and at the same time gives results which approximate closely to those obtained with high speed relays.

Reverting to the circuit operation, at theend of the train of impulses, relayA remainsheld over the callingsubscribers lqop,.and at contact al maintains relay B. Due to the opening of the 1 a resultof each subsequent impulse train and on the completion of dialling, relay A is maintained connected to line via the'ballast lamp BRA and vIi the right-hand windings of the repeating coil.

Conversation may now proceed between the callingand called parties.

. ;'It will be appreciated that if the subscribers I line isinot directly connected through t the pubhe exchange when a call is originated, then relays A and Bbn operating on the removal of the telephone receiver by the calling subscriber will extend a direct current loop calling signal throu h to the P. B. X board, after which the "call may be set up at the will of the operator either by herself or by the subscriber in the manner described. i

If the P. B. Xoperator wishes to effect a call to the distant subscriber, she connects ringing current to the incomingleft-hand negative and positive conductors and, since all relays in the auxiliary equipment shown willbe normal, this currentextends from' the negative line over armatures bl and ai; upper left hand winding of the repeating coil, comparatively low resistance YA, condenser QA, lower .left hand winding of the repeating coil back to the positive line. A similar current isthereupon induced in the righthand windings of the repeating coil and extends over the external line to ring the distant subscribers bell. The efiect is similar if an incoming call is received at a time when thesubscribers line is connected through to the main exchange.

It willb noted, that in order to revent the impulse repeating relay A from respondingto this ringing. current dry-platecopper oxide or selenium rectifiers MBA and MRB are connected series therewith. Such dry-plate rectifiers present. a very high resistance both in the conductive and in the non-conductive direction when very smallv'oltages are. applied thereto, the difference between the resistance in the conductive and non-conductive directions rapidly becoming ,more prominent as thevoltage applied thereto is iecr s d- 1 the Pr s n i um tanc th otential impressedacross condenser QB dueto the induction of the ringing current in the righting. When relay A s operated under battery hand windings of the repeating coil is f such small value that the rectif ers present a high impedance and thus prevent relay A from operatfeeding conditionsih owever, both rectifiers offer a low resistance path to the particular flow of denser QC and resistance :YBfwhichare conn w a r he. i llleef eet ns a a u c2 of relay A are provided for spark'quenching and inductive voltage reducing purposes.

7 v WhatI claim as new and desire to secure by LettersPatent is:

1. In an impulse repeater, an incoming line,

an. u ing l ne, a ba lastresistor havin a nonl near resistance characteristic, an impulse, re-

ceiving relay, a source of direct current connected to said line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said line, said relay responsive to interruptions in the flow of said current, a contact on said relay effective to repeat said interruptions in said outgoing circult, and means for short-circuiting said resistor during the response of said relay to such interruptions.

2. In an impulse repeater, an incoming line, an outgoing line, a ballast resistor having a non linear resistance characteristic, an impulse receiving relay, a source of direct current connected to said line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said line, said relay responsive to interruptions in the flow of said current, a contact on said relay effective to repeat said interruptions in said outgoing circuit, and means for connecting said source to said incoming line over the winding of relay but independently of said resistor during the response of said relay to such interruptions.

3. In an impulse repeater, an incoming line, an outgoing line, a ballast resistor having a nonlinear resistance characteristic, an impulse receiving relay, a source of direct current connected to said line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said line, said relay responsive to interruptions in the flow of said current, a contact on said relay effective to repeat said interruptions in said outgoing circuit, a slowto-release relay, means controlled by said impulse receiving relay for operating said slow-torelease relay responsive to the first interruption of a series of interruptions and maintaining said slow-to-release relay operated throughout said series, and contacts on said slow-to-release for shirt-circuiting said ballast resistor so long as said slow-to-release relay remains operated.

4. In an impulse repeater, a repeating coil having a primary winding and a secondary winding, two condensers, an incoming line and an outgoing line, means connecting said primary widing and one of said condensers in series across said incoming line, means connecting said secondary winding and the other of said condensers in series across said outgoing line, a ballast resistor, an impulse receiving relay, a source of direct current connected to said incoming line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said primary line, said relay responsive to interruptions of said current, a contact on said relay connected in said outgoing line and effective to repeat said interruptions therein, and

means for connecting said source to said incoming line over the winding of said relay but independently of said resistor during the response of said relay to such interruptions.

5. In an impulse repeater as claimed in claim 4, means including said contact for short-circuiting said secondary winding before said contact interrupts said outgoing line.

6. In an impulse repeater as claimed in claim 4, means normally short-circuiting said contact, and means controlled by said relay for removing said short-circuit during response of said relay to said interruptions.

'7. In an impulse repeater as claimed in claim 4, a rectifier in series with the winding of said relay thereby to render said relay non-responsive to alternating current applied to said outgoing line and induced into said incoming line by said repeating coil.

8. In an impulse repeater, a repeating coil having a primary winding and a secondary winding, two condensers, an incoming line and on outgoing line, means connecting said primary winding and one of said condensers in series across said incoming line, means connecting said secondary winding and the other of said condenser in series across said outgoing line, a ballast resistor, an impulse receiving relay, a source of direct current connected to said incoming line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said private line, said relay responsive to interruptions of said current, a contact on said relay connected in said outgoing line and effective to repeat said interruptions therein, a second relay, means controlled by said first relay for operating said second relay responsive to the first interruption of a train of interruptions and for maintaining said second relay operated throughout said train, and contacts on said second relay effective, so long as said second relay remains operated, to short circuit said ballast resistor and to short circuit said secondary winding.

9. In a circuit for receiving impulses at times and. speech currents at other times, a line, a ballast resistor having a non-linear resistance characteristic, an impulse receiving relay, a source of direct current normally connected to said line over said resistor and the winding of said relay in series, thereby to cause current from said source to traverse said line, said relay responsive to impulses in the form of interruptions of said current, and means for connecting said source to said lines over the winding of said relay but independently of said resistor during the response of said relay to said impulses.

CHARLES EDMUND BEALE. 

